Microphone as a blow switch

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adityabhandari54

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Hello,
I am designing a circuit which shall turn a device ON or OFF by blowing on it. I have a circuit in the form of a counter where in when a switch is pressed, the count is incremented, and i have the relay connected to the LSB of IC 4017. So each time i press a switch, the LSB turns from 0 to 1 or vice-verse and this signal is given to my relay to turn it ON or OFF. I want to modify this circuit to blow activated in stead of switch, so can a microphone be used

Regards,
Aditya
 

Yes it can be used. All you need is a microphone, couple of transistors, a capacitor and a pot for adjusting dB level. Connect two transistors, say BC547, as a darlington pair, connect a pot of 100k or 500k with vcc to mic, then mic to gnd. Feed the pot output to a ceramic cap of 10nF, then to the darlington pair gate, and feed the emitter to your counter switch. Adjust the pot for your desired noise level.

Google have a lot of reference designs for microphone.
 


A 555 can be used, and a common "electret" microphone with 12 V DC bias via a 20 kOhm resistor generates more than 0.5 V pulse if you blow over it. Use a 555 as a monostable multivibrator.
 

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